Effect of Negative Stiffness Content on the Periodic Motion of Nonlinearly Coupled Oscillators

The linear and nonlinear stiffness coupling forces in dynamical oscillators are usually dominated by positive stiffness components. Therefore, plotting the resultant force in y-axis with respect to the change in displacement in x-axis results in an odd symmetry in the first and third quadrants of the xy-plane. However, the appearance of negative stiffness content in coupling elements between dynamical oscillators generates a force that can be dominated by an odd symmetry in the second and fourth quadrants. The underlying nonlinear dynamical behavior of systems employing this kind of force has not been well-studied in the literature. Accordingly, the considered system here is composed of two linear oscillators that are nonlinearly coupled by a force of which the negative stiffness content is dominant. Therefore, the underlying dynamical behavior of the considered system in physical and dimensionless forms is studied on the frequency-energy plots where many backbone curves of periodic solution have been obtained. It is found that within a wide range of nonlinear frequency levels, the nonlinear coupling force is dominated by a strong negative stiffness content at the obtained frequency-energy plots backbones.

Multiphysics Modeling Simulation and Optimization of Aerodynamic Drum Magnetic Separator

Aerodynamic Drum Magnetic Separator (ADMS) uses an adjustable air flow to enhance the separation of magnetic particles from gangue. In order to explore the matching relationship between the magnetic field, the flow field, and the gravity field, as well as the capture and separation behavior of particles under the action of multi-physics, a related simulation model is established using the finite element software COMSOL Multiphysics and the accuracy of the simulation results is verified by measurement, formula calculation, and magnetic separation experiment. The trajectories and capture probabilities of particles in different magnetic fields and flow fields are calculated, as well as the critical airflow velocity corresponding to a specific capture probability. In addition, the magnetic field characteristics and particle capture effect of N-S alternate arrangement and N-N homopolar arrangement are compared by optimizing the permutation of magnetic poles. This model may provide a reference for the accurate control of magnetic separation enhanced by a coupling force field.

A Model for Evolutionary Structural Plasticity and Synchronization of a Network of Neurons

A model of time-dependent structural plasticity for the synchronization of neuron networks is presented. It is known that synchronized oscillations reproduce structured communities, and this synchronization is transient since it can be enhanced or suppressed, and the proposed model reproduces this characteristic. The evolutionary behavior of the couplings is comparable to those of a network of biological neurons. In the structural network, the physical connections of axons and dendrites between neurons are modeled, and the evolution in the connections depends on the neurons’ potential. Moreover, it is shown that the coupling force’s function behaves as an adaptive controller that leads the neurons in the network to synchronization. The change in the node’s degree shows that the network exhibits time-dependent structural plasticity, achieved through the evolutionary or adaptive change of the coupling force between the nodes. The coupling force function is based on the computed magnitude of the membrane potential deviations with its neighbors and a threshold that determines the neuron’s connections. These rule the functional network structure along the time.

Virtual Experiments of Particle Mixing Process with the SPH-DEM Model

Particle mixing process is critical for the design and quality control of concrete and composite production. This paper develops an algorithm to simulate the high-shear mixing process of a granular flow containing a high proportion of solid particles mixed in a liquid. DEM is employed to simulate solid particle interactions; whereas SPH is implemented to simulate the liquid particles. The two-way coupling force between SPH and DEM particles is used to evaluate the solid-liquid interaction of a multi-phase flow. Using Darcy’s Law, this paper evaluates the coupling force as a function of local mixture porosity. After the model is verified by two benchmark case studies, i.e., a solid particle moving in a liquid and fluid flowing through a porous medium, this method is applied to a high shear mixing problem of two types of solid particles mixed in a viscous liquid by a four-bladed mixer. A homogeneity metric is introduced to characterize the mixing quality of the particulate mixture. The virtual experiments with the present algorithm show that adding more liquid or increasing liquid viscosity slows down the mixing process for a high solid load mix. Although the solid particles can be mixed well eventually, the liquid distribution is not homogeneous, especially when the viscosity of liquid is low. The present SPH-DEM model is versatile and suitable for virtual experiments of particle mixing process with different blades, solid particle densities and sizes, and liquid binders, and thus can expedite the design and development of concrete materials and particulate composites.

Influence of bone conduction transducer type and placement on ocular and cervical vestibular evoked myogenic potentials

Evaluating the effectiveness of different bone conduction (BC) transducers with controlled coupling force to elicit cervical and ocular vestibular evoked myogenic potentials (cVEMPs, oVEMPs) in healthy subjects by comparing response rates, amplitudes, latencies, thresholds and asymmetry ratios. Prospective experimental study including healthy participants. VEMPs were measured to different stimulation modes; the BC transducer coupling force was controlled to 5.4 (± 0.5) Newton. cVEMPs: to bone conducted vibration (BCV) with the B81 transducer on the mastoid; oVEMPs: to BCV with the B81 on the mastoid, BCV with the B81 on the forehead, and BCV with the Mini-Shaker 4810 on the forehead. Air conducted sound (ACS) with insert earphones was used as reference. Data of 24 normal subjects (mean age 25.3 (± 3.0) years) were analyzed. ACS and BCV with the B81on the mastoid evoked cVEMPs in 100% of ears. The highest oVEMP response rates were obtained with the B81 on the mastoid (83–92%), the lowest with the B81 on the forehead (17–22%). The Mini-Shaker elicited lower response rates (65%) compared to results from the literature without coupling force control and compared to ACS (78–87%). Amplitudes were higher for BCV than ACS. ACS and BCV on the mastoid caused higher asymmetry compared to BCV forehead stimulation. The B81 was feasible to elicit VEMPs with mastoid placement and can be used as an approved medical device to measure BCV VEMPs in a clinical set-up. Normative asymmetry values have to be established due to higher variability for mastoid stimulation.

Influence of bone conduction transducer type and placement on ocular and cervical vestibular evoked myogenic potentials

Purpose: Evaluating the effectiveness of different bone conduction (BC) transducers with controlled coupling force to elicit cervical and ocular vestibular evoked myogenic potentials (cVEMPs, oVEMPs) in healthy subjects by comparing response rates, amplitudes, latencies, thresholds and asymmetry ratios.Methods: Prospective experimental study including healthy participants. VEMPs were measured to different stimulation modes; the BC transducer coupling force was controlled to 5.4 (±0.5) Newton. cVEMPs: to bone conducted vibration (BCV) with the B81 transducer on the mastoid; oVEMPs: to BCV with the B81 on the mastoid, BCV with the B81 on the forehead, and BCV with the Mini-Shaker 4810 on the forehead. Air conducted sound (ACS) with insert earphones was used as reference.Results: Data of 24 normal subjects (mean age 25.3 (± 3.0) years) were analyzed. ACS and BCV with the B81on the mastoid evoked cVEMPs in 100% of ears. The highest oVEMP response rates were obtained with the B81 on the mastoid (83 – 92%), the lowest with the B81 on the forehead (17 – 22%). The Mini-Shaker elicited lower response rates (65%) compared to results from the literature without coupling force control and compared to ACS (78 – 87%). Amplitudes were higher for BCV than ACS. ACS and BCV on the mastoid caused higher asymmetry compared to BCV forehead stimulation.Conclusion: The B81 was feasible to elicit VEMPs with mastoid placement and can be used as an approved medical device to measure BCV VEMPs in a clinical set-up. Normative asymmetry values have to be established due to higher variability for mastoid stimulation.

Lower excitons strong light matter interaction in plasmonic tweezers

Plasmonic nanocavity has been an excellent platform to study light matter interaction under ambient conditions and within sub-diffraction volumes. However, controlled strong light matter interaction in the plasmonic system has rarely been reported. Here, we design a plasmonic tweezers, which can trap a molecular J-aggregates, and be a plasmonic cavity to investigate the strong light matter interaction. We use finite-difference time-domain methods and Maxwell stress tensor to evaluate the optical response and the trapping performance. With the help of coupled oscillator model and virtual excitons theory, we analyze the strong coupling progress in lower excitons system, we further introduce a `coupling force' parameter to characterize the relationship between the optical force and model volume in the coupling system. The proposed method offers a way to locate a molecular J-aggregates in a plasmonic tweezers for investigating optical force performance and strong light matter interaction.

Modelling, Analysis and Identification of the Parallel and Angular Misalignments in a Coupled Rotor-Bearing-AMB System

The standard techniques used to detect the misalignment in rotor systems are loopy orbits, multiple harmonics with predominant 2X component, and high axial vibration. This paper develops a new approach for the identification of misalignment in coupled rotor systems modelled using 2-node Timoshenko beam finite elements. The coupling connecting the turbine and generator rotor systems is modelled by a stiffness matrix, which has both static and additive components. While the magnitude of static stiffness component is fixed during operation, the time varying additive stiffness component displays a multi-harmonic behaviour and exists only in the presence of misalignment. To numerically simulate the multi-harmonic nature coupling force/moment as observed in experiments, a pulse wave is used as the steering function in the mathematical model of the additive coupling stiffness (ACS). The representative TG system has two-rotor systems, each having two discs and supported on two flexible bearings - connected by coupling. An active magnetic bearing (AMB) is used as an auxiliary bearing on each rotor for the purposes of vibration suppression and fault identification. The formulation of mathematical model is followed by the development of an identification algorithm based on the model developed, which is an inverse problem. Least-squares linear regression technique is used to identify the unbalances, bearing dynamic parameters, AMB constants and importantly the coupling static and additive stiffness coefficients. The sensitivity of the identification algorithm to signal noise and bias errors in modelling parameters have been tested. The novelty of paper is the representation and identification of misalignment using the ACS matrix coefficients, which are direct indicators of both type and severity of the misalignment.